text:
How does an airplane move itself in the runway?
Basically do they move themselves using their powerful jet/propeller engines to propel themselves forward or do they just use an engine that powers the wheels used for landing?
I'm not really asking about planes that are readying for takeoffs just the ones that move on the ground like a car would.

The power to move an aircraft from point A to point B on an airport is provided by the same engines that power it in flight unless you hook up a tug, in which case the tug provides the power. There have been experimental developments that provide power to the main landing gear wheels, but there have never been any real implementations of these systems. Small single-engine aircraft can be moved by hand.

It's common for multi-engine aircraft to taxi using one or two engines instead of all of them, to save fuel.  However, all the engines must be started, warmed up and power tested shortly before takeoff.  For small aircraft at small airports, the taxi from the apron to the runway is just about enough to warm the engines up properly, and the runway threshold is the best location for the power test.

For small airplanes, you can use a towbar and move it yourself.  Especially if you're just moving from one place to another on the ramp, or into/out of a hanger.

Planes use a tiller. A tiller is a piece of equipment beside the yoke (at least, on Boeing aircraft) that looks like this. It moves the wheels while the pilots control the engines to provide thrust. I found this thread that should provide more answers to your question.

The tiller is used for steering the nosewheel, rather than for propulsion as I think this question was about.  Most small planes link the nosewheel steering to the rudder pedals, and some very large aircraft (eg. 747) have a second tiller to steer the main landing gear as well, allowing easier crosswind landings.

@Chromatix The 747 has a tiller on the captain's side and one on the first officer's side, thus two tillers. However, both are for controlling the nose gear. They move in concert. The main gear cannot be canted like, say, the B-52 for crosswind landings.


text:
Why do flights from Tel Aviv to Honolulu go west?
Out of curiosity, my kid was looking at flights from Tel Aviv (TLV) to Honolulu (HNL) and noticed that they all fly west, with stops in the lower 48 (contiguous U.S.). This surprised me:

Tel Aviv's longitude is about 35°E and Honolulu's is 158°W, so the flight eastward passes only 167° of longitude.
There are places to stop along the way that allow flights in from Israel (e.g., Moscow, I suppose).
Flying eastward is faster.

Why do flights from Tel Aviv to Honolulu go west? And if they're going west then why through the lower 48 rather than, say, Anchorage (ANC), which is sorta on the way?

Can you add an example of such a flight? After a quick search, I cannot find a single flight from TLV to HNL (under the same flight number).

I didn't check, my kid did, but those were the routings that the airline sites gave: but maybe not under the same flight number. Should I reword the question to ask why airlines route people that way, rather than as why flights go that way?

If it's not a single flight number then the answer just depends on which direct connections exist and that is simply based on passenger demand. There are also connecting flights going east, but they have 2 stops rather than 1 (e.g. via Hong Kong and Tokyo).

@Bianfable:  FlightConnections says it's currently possible to fly TLV–NRT–HNL, but the first leg only operates 3 days a week and the two airlines (El Al & Hawaiian) don't code-share.  COVID restrictions may also make this itinerary unfeasible.

Also, if we're talking about connecting flights rather than a single flight, then it's no surprise that they don't use the TLV–ANC–HNL route;  it would require there to be a market for a stand-alone TLV–ANC route, which seems unlikely to me.

Hmm, west would be into the prevailing wind, but would have fewer exposure to various airspace sovereignties.

Are there actually enough people in Israel who want to go to Hawai'i (or vice versa) to justify a direct flight?  Whereas you might have many more people who want to go to places in the US, or from those places onwards.

Voting to leave open, airline flight routes are subject to economic motives, not to opinion.

Airline routes are also subject to operational restrictions (ETOPS for example), this is definitely on topic here.

ETOPS have nothing to do with this question as many airlines operate Eastbound flights between Tel Aviv and Asia and between Asia and Honolulu. You can fly Eastbound now, but the connection times and code sharing may not be to your liking.

@MikeSowsun the 2 engine regulation might not apply but the principle of staying near friendly airports would. Going through the lower 48 and EU means there is always an airport nearby at the cost of 3.5 Mm (megameters) more flight instead of the Great Circle route which would be over wilderness for a greater portion of the flight.

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How does a VOR or a VORDME affect the coding decision between CF or IF-TF respectively?
I was reading of the following case in ARINC 424-17 spec. Unfortunately the image is copyrighted and I can't paste it here, so here is a low(er) quality image of mine replicating the situation:

The text says that the path after the VI has to be coded as a CF if the XYZ is a VORDME but if the navaid is VOR only then it should be an IF-TF sequence. My question is not why is that sequence by how does the collocated DME affect the decision? The document mentions

This will allow a segment to be constructed, from one fix to the next fix, using an “intercept” where coding would otherwise not be possible.

But it doesn't explain why is it "not possible" to code this path as a CF if the station doesn't have DME. How does DME help here? In my mind, FOOBR is on a radial, let's say 55 from XYZ so if the airplane intercepts and follows this radial it will arrive to FOOBR, no DME involved. Is there something that I'm missing here?

VI vector to intercept
CF course to fix
IF initial fix
TF track to fix
Clarification:
Ralph J asked "what's the difference between CF and TF paths?" That's actually a good question. The spec is quite laconic:

Course to a Fix or CF Leg. Defines a specified course to a specific database fix.
Track to a Fix or TF Leg. Defines a great circle track over ground between two known databases fixes.

To my understanding, TF is more accurate as the course is derived from the previous fix while CF requires the course and recommended navaid to be coded in the aircraft's database, hence making the TF a simpler choice when available.

Makes sense (as much as it can). Is the start of the VI leg at all related to the XYZ facility?

@RalphJ Not sure at all! The example doesn't specify. VI path legs can have a recommended navaid set but it's not mandatory. It could be set to "XYZ". It's an SID if it makes any difference.

@RalphJ The normal use of the VI-CF is a departure procedure construct. The VI leg normally follows a VA leg (HDG to an Altitude) from the runway; e.g.; Fly runway HDG, at 400 ft AGL turn to HDG 095, intercept outbound 030 radial of XYZ, then to FOOBR...  The actual path of the VI leg can vary due to climb rate (when you reach 400 ft) and winds as heading legs don't compensate for wind.

First; you have to understand that ARINC 424 is an industry standard.  It is not regulatory.  The regulatory documents are published by RTCA (and EUROCAE in the EU).  The basic database coding requirements of it are generally well accepted and used by the industry as those are essential to its primary function of interoperability.  But there's a lot of flexibility in how strictly developers follow the standard.
The example you give is one of application of the standard.  Both of the leg combinations are valid, though the IF-TF is preferred.  Note that ARINC 424 uses the word 'should' and not 'shall'.
Having worked FMS, I can say that the VI-CF could be coded but there are potential issues if XYZ is not a VOR/DME.  How is FOOBR defined if there's no DME?  It would have to be defined as an intersection with a radial from another VOR and the XYZ radial or as a Lat/Lon fix.
If it's a Lat/Lon fix, you can't reliably use the CF leg to get to it even if it's nominally on the radial as the radial error is quite large and could result in 'missing the fix' while flying the radial.  And since the Lat/Lon fix is the RNP standard, the preferred leg type would be an IF-TF leg with the IF at XYZ.
If FOOBR is an intersection, it can be workable once you are established on the CF leg - by tracking the crossing radial.  But the VI leg intercept is a floating fix which complicates the path generation as the relative positions of the intercept and FOOBR are not easily computed.  That problem is much simplified if FOOBR is a Lat/Lon.
In my experience, I would expect the CF leg to be coded as a IF-TF.  That provides fixed start and end points and a much simplified intercept computation.  And it wouldn't be unusual for an FMS to convert the the original CF leg (based on the VOR/DME) into a TF leg.

If it's a Lat/Lon fix [...] the radial error is quite large and could result in 'missing the fix' [...] I know I'm risking to ask a new question inside a comment but here it goes: if it's a Lat/Lon fix, wouldn't the FMS use GNSS/GPS to get to it? And thanks for the answer anyway.

Yes.  It would use GPS or GPS/IRS as that's primary position source in an RNP system, which is why the TF leg would be preferred. The TF leg is defined as a geodesic path between two WGS84 defined fixes. The CF leg is tied to the broadcast signal of the VOR. The only place the CF leg is accurate to the same level of a WGS84 fix is at the VOR. Early GPS non-precision approaches were just overlays of the old VOR or NDB approach. It looked like you were flying the VOR radial, but it was all TF legs. On many, you could see a difference of 1 or 2 deg between the charted course and the GPS track.

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What is the reason behind updating the radar tracks on the CWP in chunks instead of updating them all at once?
Some time ago, I noticed that the controller's screen (CWP) of a particular system in a European ACC. was not updating all the visible tracks at once but it was following this pattern:
The screen appeared as if it was split in invisible rectangles. Starting from the upper left corner, only the tracks in a particular rectangle were updated at a time. Then immediately (I think, there might have been some millisecond delay but I couldn't tell for sure) the next rectangle at the right was updated and once all the rectangles on the row were done, the "scanner" moved to the next raw and so on and so forth.
I've seen a similar pattern in another system (in Europe) as well. Is there some technical reason behind this seemingly complex design? eg. could it be the way the surveillance data processing system (SDPS) functions?

@ymb1 small to moderate I would say. Approximately 80.000 km^2 (around the size of Maine state). But anyway I'm afraid I will have to reword the question. I don't know if this behavior comes from the CWP, or the radar data processor, or any other system and this is not depicted in the question.

Was this in the US? If so, was it terminal or enreoute? Did you see it firsthand or was it a video we can see?

@RetiredATC No Europe and I saw it firsthand. It was ACC (en-route). If I had a video I would have posted it :) I will update the question.

I cannot comment on Eurocontrol radar display systems, but in the US, radar data processing is divided into 10NM squares called sort cells. Each sort cell has a preferred radar, normally (but not always) associated with the nearest radar site. Each cell will generally have a second and sometimes a third radar site to provide data if a satisfactory return is not obtained from a higher priority radar.
As the radar antenna turns, the data is digitized and sent to the facility, where ERAM (the enroute ATC computer system) compiles the information and presents it on the controller's display. Since the updates follow the rotation of the radar, you can see a "sweep," but it is not as pronounced as some of the older terminal radar displays.

In the Terminal environment we now use Fusion mode in STARS, which combines ASR, ARSR, and ADS-B data to create an "average" or "best-guess" for each track. All tracks are updated simultaneously each second (even tracks without ADS-B, which are essentially coasted until the next radar update). If we switch from Fusion to single-sensor mode the targets are not updated simultaneously; the "sweep" is very noticeable even though the sweeping arm running around the scope is no longer present.

Anyway, this is all very interesting but (as you say) neither of us can speak to Europe. Your description of ERAM's sort boxes is at least a little bit similar to what OP describes, but it would still be a clockwise rotation for the most part, not a right-to-left row-by-row update.

@randomhead If the software is designed to update all the data in each sort cell, send that output to the scopes, and then move to the next sort cell, that’s exactly what you’d see. And I’d assume that’s why the sort cells exist in the first place: divide the multi-input correlation task into more manageable chunks.

Also this obviously is not about eurocontrol systems but some other facility in Europe


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What is the minimum thrust needed to takeoff?
In passenger airplane how much thrust is required to takeoff? What factors does it depend on?

You want exact lbs.ft or % or for B747 or Cessna 172 or just principle behind it?

0, provided sufficient wind

Elevation (pressure), temperature and weight are the three that come to mind.

0 provided the runway slopes enough. There are glider videos that literally takeoff by rolling down hill

You need at least enough thrust to keep the airplane flying at the speed of minimum drag. This is quite a bit higher than the minimum flight speed, so you should add something to quicken the acceleration to this point. Also, you want to climb eventually, so you better add some more thrust.
Normally, the static thrust of an airliner is at least a quarter of its weight. If the airliner is empty, this can become as much as half of the weight.
One reason is altitude capability: Since thrust goes down with the density of air, the static thrust in the cruise altitude is only a quarter of sea level thrust. The thrust of a modern high-bypass-ratio engine drops with speed, so at cruise speed and altitude, thrust is roughly a sixth of sea level static.
The second reason is safety: The take-off should be continued even after one engine fails in the late acceleration phase. Now a normally two-engined plane has only half as much thrust available and should still get into the air, so it doesn't crash into whatever follows at the end of the runway.
The thrust needed to sustain flight is about 1/18 of aircraft weight, and if you factor in the multiples given above, you will notice that if the aircraft can fly at full thrust in cruise, this fits nicely with a static sea level thrust force equivalent to one third of its weight force.
The factors for take-off thrust are:

Runway length: Short runways need more excess thrust for faster acceleration.
Runway elevation: Higher places have less dense air, so more speed is needed to get airborne, and less thrust is available from the engines than at sea level.
Runway slope. Taking off downhill is equivalent to having a little extra thrust.
Air temperature: Colder air is denser, so minimum speed is lower and the engines develop more thrust.
Wind speed: A headwind is equivalent to starting the takeoff run at this speed.
Minimum flight speed: A low wing loading and low-drag flap settings reduce the speed at which the aircraft can take off.

The 1/18 is typical required thrust for airliners at best glide speed, but at $V_2$ it will be higher. I'd say perhaps 1/12–1/10, but I haven't seen those values quoted anywhere publicly, so that's just a guess based on simulator that estimates behaviour from geometry and some fudge-factors. And don't forget some reserve to be able to actually climb, not just sustain flight.

@JanHudec: True, especially with flaps set for takeoff. But I didn't want to imply that the 1/18th applies for takeoff. If the runway is long enough, though, the minimum thrust needed for takeoff would be indeed about 1/18th of weight.

Only very theoretically. You'd need to lift off to the ground effect (where drag is lower) and accelerate in ground effect to best glide speed (that is something like 260-280 knots).

@JanHudec: I do all acceleration on the ground and lift off just when reaching minimum drag. Of course, climbing would require more thrust, but if the minimum is asked for, this is it. Only the runway needs to be long enough, and I need to disregard maximum tire speed.

a) are you sure wheels would still provide less drag at 260 knots than wing-in-ground-effect (or at least wing out of ground effect) and b) are you sure the tires would not blow up long before you got to that speed?

@JanHudec: a) absolutely yes! The airframe has half as much drag than in flight, that leaves a lot of drag for the wheels before flying is better; b) they probably would. It needs special tires for that speed (like those on the Space Shuttle), and the really fast cars have simple aluminum disks for wheels.

The amount of thrust necessary is the force required to accelerate the aircraft to take off speed, a speed which allows the wings to generate enough lift to sustain the aircraft in the air.
Factors include

aircraft weight
runway condition (length, slope, dry/wet)
flaps configuration
head wind component
If it's a multi-engine aircraft, the ability to safely get airborne in the event of a single engine failure is considered as well.

If by "amount of thrust", you mean the acceleration force: engine power ranges from 160hp on small propeller planes to thousands of pounds in turbine jets (Boeing 777's engine is rated at 417kN). In most GA planes, takeoff power = full power. In larger aircrafts, typically it is slightly below full power to save engine wear.

Note that "thrust" is not used to get an airplane off the ground. "Lift" is used to get it airborne and counteract the "weight". "Thrust" is produced by the engine(s) to propel the plane forward, "lift" is created by the wings.

Most airliners are actually in the tens of thousands of pounds per engine. The 777 is even more, with up to 115,000 lb. per engine (rated... it's been tested to something like 127,000 lb., IIRC.) Fun fact: A single engine from the 777-300ER is sufficiently powerful to fly a DC-9 straight up while still accelerating.

So essentially a 777-300ER is an overweight DC-9 VTOL?

Notwithstanding exceptions and certain details the operator can decide about, generally the minimum thrust required to satisfy EASA (and FAA) regulations on takeoff performance for civilian jet aircraft is that which allows for a given weight, aircraft configuration, runway, and set of environmental conditions to

Accelerate to the value of V1 speed pertinent to that specific
takeoff with all engines operating
Either reject the takeoff from V1 speed with either all engines
operating or one engine inoperative within the allowed distance for
the stop case or
Continue the takeoff from V1 speed with one engine inoperative,
accelerating to VR and V2 speeds pertinent to that specific takeoff
within the allowed distance for the takeoff case
Climb out from the runway at V2 speed while meeting a minimum climb
gradient defined in the regulations (depending on the number of
engines)
Clear all obstacles under the takeoff flight path by a certain
predetermined margin
Reach a minimum height for flap retraction or attain clean
configuration and associated speed within the maximum time limit for
engine operation at takeoff thrust (usually either 5 or 10 minutes)

This is a rather simplified, condensed version of various paragraphs in EASA CS 25 (Certification Specification for Large Aircraft) and EASA Air Operations regulations, chapter POL (Performance and Operating Limitations - e.g. CAT.POL.A.205 details takeoff distance requirements). For more details, I'm afraid that actually reading the regs is as good as it gets...

It all comes down to Newton's second law of motion in that:
$$F= m \cdot a$$
The trust required for a 70 m/sec. 10.000 kilos takeoff speed and weight with an acceleration of 2g is: 20 Kilo Newtons, it will take 35 seconds and 1225 meters of runway to become airborne .At the moment airplane manufacturers have to trade off Power and Speed to the best fuel economy. but with propellers a max speed is about 662 K hr ( SAAV 2000 ) and jets with a optimun speed is 880 k hrs. Both do not travel at the optimun speed for ANY airplane of around 700 kms per hour wich is where induced drag and atatic drag are at their lowest so a propeller airplane is slow and a jet is fast and the penalty is fuel consuption because the jet have travel at the speed of combustion in the engines and propellers can not be made bigger than they are now (speed of sound limits their size at the tips)

That's a lot of trust... :)

2g = around 20m/s2 so the time to accelerate will be more like 3.5 seconds not 35seconds

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What is the meaning of these slang terms used in ATC?
I have heard some slang terms used mainly by ATCs:

follow the black holes
taxi not too deep
how is your ride

What do they actually mean and are there others?

The first two seem unusual (at least to me), where exactly did you hear them? And did you hear them in English or another language? The last one is ATC asking for a PIREP to find out what the flying conditions are like, possibly because another aircraft nearby is experiencing turbulence and is looking for a better (smoother) level to fly at.

Yes, the first 2 really are unusual, that's why I used the word SLANG. I have hear on QRG from MIA and ORL. And, they were heard in English, for sure.

What country are we talking about here?

About these phraseology? The USA, on MIA and ORL.

Do you have any recordings, or a link to liveatc.net? If we could hear the complete conversation then it might be clearer.

Something like these: During taxi phase: FOLLOW THE BLACK HOLES (it seems to be, follow the twin engine aircraft, leading you); CLEARED PUSHBACK, NOT TOO DEEP, THERE IS A TRAFFIC PASSING BEHIND YOU (it seems to be, turn right or left soon, to avoid traffic, passing right to left or vice versa)...I don't know.

Follow the black holes
I have no idea about this one. I looked at the airport diagrams and arrival/departure procedures for MIA, MCO and ORL and I couldn't see anything that seems like it could be confused with the words "black hole". So, I have two guesses:

It's the code name for a set of local taxi instructions
As you suggested, it's the controller's slang for "the twin-engine aircraft in front of you", i.e. the black holes are the exhausts

I think the second possibility is very unlikely, though. A controller at a major international airport - which implies many pilots with English as a second language - is unlikely to use non-standard phrasing for a critical instruction like which aircraft to follow.
Taxi not too deep
This one is a lot clearer from the updated comment you gave: "CLEARED PUSHBACK, NOT TOO DEEP, THERE IS A TRAFFIC PASSING BEHIND YOU". That's exactly what it sounds like: the aircraft was cleared to push back from the gate, but the ground controller was warning the pilot not to push back too far ("too deep") because of another aircraft passing behind.
How is your ride?
This one is ATC asking a pilot for a PIREP. That could be because another aircraft nearby is in turbulence and trying to find a smoother altitude, so the controller asks other aircraft about the ride at their flight levels. Or, since you heard this in the US, it could be for this reason, from the AIM section 7-1-20:

FAA air traffic facilities are required to solicit PIREPs when the
  following conditions are reported or forecast: ceilings at or below
  5,000 feet; visibility at or below 5 miles (surface or aloft);
  thunderstorms and related phenomena; icing of light degree or greater;
  turbulence of moderate degree or greater; wind shear and reported or
  forecast volcanic ash clouds.

Are there other examples of slang?
I'm sure there are, although slang in general is discouraged because of the potential for misunderstandings. The FAA has a pilot/controller glossary to make sure that everyone is using the same words and phrases as far as possible (ICAO provides one too), but that doesn't mean that people always stick to it 100% of the time. Ex-military pilots - and controllers - in particular sometimes use some military terminology (e.g. bingo fuel) out of habit (presumably) even though they really shouldn't in a civilian setting.

"Follow the black holes" doesn't sound like a good thing. A "black hole approach" is an optical illusion during night approaches when there isn't any light between you and the approach array. You tend to and up flying too low and crash short of the runway. So, "following the black hole" sounds to me like ATC is telling you to believe the illusion.
"Taxi not too deep" sounds like alternate phraseology for "land as short as possible and exit quickly". ATC will give this instruction when something bigger or faster is coming in behind you.

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What is the relation between airspeed and altitude at fixed throttle setting in a private jet?
In the world of private jets, say a G-450, at a fixed throttle setting, does it simply go faster the higher it climbs/flies?

The basic principles needed for an answer are:

Thrust varies linearly with air density.
Lift at constant angle of attack (AoA) equally varies linearly with air density.
Increasing the angle of attack from a low value will improve the lift to drag ratio (L/D), while increasing it from a higher value than the AoA at optimum L/D will decrease it.
The aircraft will settle at the point where speed equals drag and lift equals weight. If the altitude change improves L/D, the aircraft has excess thrust to fly faster.
Due to the atmospheric lapse rate, the speed of sound decreases with altitude.
Above a certain Mach number ($M_{dd}$ = drag divergence Mach number), drag increases nonlinearly over dynamic pressure.

Now the answer depends on where you start:

Low altitude, moderate throttle setting: The aircraft will speed up, because it was flying at a low AoA in dense air. Climbing brings it closer to the polar point of optimum L/D.
Low altitude, high throttle setting: If the aircraft flew at close to its $M_{dd}$, climbing will put it in colder air where it needs to fly slower to maintain the same Mach number. Depending on the starting speed, the aircraft might slow down.
High altitude, moderate throttle setting: Now the thrust decrease with altitude will dominate the equation, because the aircraft will fly close to its optimum polar point. Once it flies above the AoA of minimum drag, climbing will slow it down.
High altitude, high throttle setting: If it flies above the tropopause and close to the polar point of minimum drag, the air temperature does not change with altitude, and climbing will not change flight speed. It will stay close to its $M_{dd}$. Once it flies above the polar point of minimum drag, however, climbing will again slow it down.

Probably pedantic, but isn't drag increasing non linearly over speed, even below the divergence Mach number? Is the quadratic relation between drag & speed becoming super-quadratic at the drag divergence Mach number? Basically aren't we moving from a drag coefficient that's speed independent to a drag coefficient that increases rapidly with speed? What's the functional form of this dependence?

@curious_cat: Yes, I should better have used dynamic pressure. Corrected. The drag increase is hard to put into a formula; I have seen approximations using the seventh power over speed, but in the end the behavior is only to capture completely by tabulation over Mach. Hint: This would be worth a question of its own.

Hint taken! :) First I will do some reading to ask a better question.

Simple answer: within normal operating altitudes, mostly yes, due to the thinner air causing less drag while the engines are producing approximately the same amount of thrust
Other simple answer: it depends, and there will be an optimal altitude above which the aircraft travels slower due to the engines losing thrust.
There are a lot of aspects that complicate it, but assuming you're basically asking 'at full throttle, does an aircraft travel faster at higher altitude?' the simple answer is yes, up to a point. Obviously that doesn't apply above the service ceiling, and the optimal altitude may be lower than this.
The optimal altitude will be a function of the engine performance and airframe.

As altitude increases, the primary effect on aircraft is the reduced density of the air it flies through. A reduction in air density has three key effects on flight:

Power at a constant setting decreases, because the air-breathing engines we use have less air to use for combustion and to push against.
Lift also decreases for the same reason; the aerodynamic lift surfaces (wings) are pushing less air and therefore the forces pushing the wings (and the rest of the aircraft) upward are reduced at a given angle of attack.
Drag is decreased, because less air means less friction drag and weaker wake vortices. This is usually offset somewhat by the need to increase angle of attack, which increases induced drag.

So, as the air thins, your engines produce less power, but you need less power because your drag is reduced, but that's offset by the need to pitch up to regain lost lift. The net results are an overall decrease in aircraft performance (ability to climb/turn and max speed), but (to a point) increased fuel efficiency.
One last effect is a reduction in temperature. By the ideal gas laws, cooler air is denser than warm air at a constant pressure, however the equation is dominated by the reduction in pressure.


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Why do farmers register their fields as airports?
(this seems to be primarily a US phenomenon)
So in the vicinity of my parents' place (in a rural area in Indiana), there are several registered airports within several miles' radius.  I remember when I was a kid, there were a few farmers in the area who liked to fly ultralights, and I wonder if some of these might be for that.  And some of these are listed as having certain aircraft based there.  For many of them, however, looking at their fields on Google Maps there is nothing to indicate that it is ever used for anything but growing crops--in some places there is no obstacle-free area even reasonably close to the listed runway dimensions.
What's going on here?

tax reduction/fraud maybe.

What does it mean to be registered as an airport? Do you need to involve FAA? Or maybe they are just registered as airport projects?

@mins Yes, you need to involve the FAA. Your airport information will be added to the A/FD, etc. Here's an example.

@ratchetfreak I highly doubt that taxes on a farm can be higher than an airport.

@Farhan You're assuming that tax laws are logical. That's a bad assumption. Still, though, I agree that that's not likely the reason.

A lot of farmers will fly to inspect their crops. Whether they're using an ultra light or small SEL, I believe that they need to have their "airport" registered. There's one near me (I believe it's decommissioned now) that was nothing more than grass between fields.

http://disney.wikia.com/wiki/Dusty_Crophopper

Some states may have laws about landing planes except at official airports, so if you want to keep your plane at home, you designate your field as a private airport.  I think this was true of California, back in the '70s, at least if I'm correctly remembering the comments of the farmer I worked for at the time.

Just spoke to the farmer that owns Graham Farms Airport (SN72), a grass strip in a cornfield near the sprawling metropolis of Harris, Kansas. Here it is on the sectional:

And Google Earth:

He has a Cessna 182 there. He told me he had it registered as an airport back in the 1970's, like Dave said, in case someone had an engine failure or something, atc could vector them there. He also occasionally allows people from nearby Garnett Municipal Airport (K68) to practice grass strip landings there.
He got an unexpected benefit from having it registered with the FAA several years back when the power company was planning to run a high tension line right across his landing strip. The power company refused to work with him on it so he called the FAA. Since it is officially an airport federal regulations forced them to run their line around it.

Aviation trumps power company profits!

Happy ending to that story! :)

Sounds like a great reason to have your airstrip registered! Keeps the ugly transmission lines away.

@FreeMan -- not just ugly, hazardous!  Power lines are the bane of cropduster and helo pilots...

Private airfields are not at all uncommon in the U.S., especially the rural parts (which is most of the U.S.) These are probably for crop dusting or because the owner also happens to be a private pilot and wants to keep their plane at home rather than paying the local FBO for hangar or tie-down rental. Of the ones I've seen, though, the markings vary from very simple (old tires painted white placed along the edges) to non-existent. Sometimes smaller ones can be hard to see on Google Maps, but, at least in my experience, you can usually find them if you look hard enough. They're probably easier to spot in places with a lot of trees rather than in places where the land is predominately wide-open farmland.
Here's an example of what it looks like on a Sectional Chart and on Google Maps:

One Grand Field on a Sectional Chart

One Grand Field (yes, it's literally a field) on Google Maps. The long, narrow clearing in the trees is the grass runway.
To give an idea of just how common these things can be, take a look at this sectional chart clip:

There are no less than 12 private airports here within a roughly 25 nmi x 25 nmi area, despite having two nearby decent-sized public uncontrolled airfields (one of which is home to a large flight training school,) and a class D airport (with a busy-ish Class C visible in the Northwest corner of the clip.)

They may have crop-dusters that they fly in and out of their own fields like this one. If the crops need dusting often and there is no airport nearby it may be cheaper and easier to fly from their own fields rather than spend the gas getting back and forth to a local field.
Here is a great little article that may give you some info. As to why they have them on the chart the article states,

So, if private airports are so private, why do their owners choose to have them depicted on sectional charts? Again, the reasons vary, but most owners seem to be motivated by altruism. Pilots want other pilots to have options when they fly, especially in the event of an emergency.

Some do it even when there is an airport nearby. Note the example in my answer. It's about 2 miles from an actual public airport with a 6,700 ft. runway.

@reirab Unless your emergency really needed a 6,700 ft runway and all the facilities and services that go along with it, you would probably have quite a lot of explaining to do if you disrupted commercial operations to land your microlight in an emergency, even if what you did was "legal" in terms of the regulations. (There are people still alive who have stories to tell about the time they landed their Tiger Moth at London Heathrow because they were low on fuel, put 5 gallons in the tank, paid in cash, and continued their flight, but not any more.....)

@alephzero Sorry, my comment was from before Dave expanded his answer to mention the possible use as emergency diversionary fields. I meant that some people create their own private airstrips, even when there are perfectly good public airports nearby.

@alephzero Regarding emergencies, though, it's generally better to have explaining to do than to not be alive to explain. And you will actually have more explaining to do if you land at a private airfield that isn't yours than if you land at a large, public-use airport. Still, though, that's much better than not being alive to explain. While pilots should generally be polite, if a light aircraft is in a fuel emergency and needs a runway that a 747 is currently lined up on, you can bet that that 747 is going around 100% of the time. Emergency aircraft always take precedence.

@reirab -- I wouldn't be surprised if even AF1 would make circles somewhere for a little bit to let a rather...smoking C172 get back on terra firma.

Also: another reason to chart 'em -- it gives other pilots operating in the area a clue that they have to look out for airplanes operating in the vicinity of those airports, and that there's a traffic pattern there they shouldn't bore through willy-nilly.

Another reason: many of them make great landmarks during daylight hours. As far as AF1, I think in most cases, they'll be wondering what said C172 is doing in their TFR in the first place. They'll probably let it land, but quite possibly with an escort or two.

Another reason might be related to the crop dusting. Presumably it isn't every farmer in the area who has a private airfield. So those who do may want to let their neighbours know where they can refuel and reload when they hire a crop duster.

Can an F15/16 fly slowly enough to escort a C172?

@DanNeely: I remember 2003 when someone flew a hijacked HK 36 TC over Frankfurt city, and they did sent up a pair of F4 Phantoms to force the pilot off. Didn't work out that well -- the F4's couldn't slow down enough, and a close pass would've swatted the micro right out of the sky.

@DanNeely No they can't go that slow, but an A10 Thunderbolt does very nicely as interceptor in such a case. And you can always send up a few Apache helicopters. They are probably doing surveillance in the neighborhood anyway when AF1 comes to visit ;-)

Having done ag application work, most ag applicators will be happy to work out of uncharted fields.  Some operators will chart their home field, particularly if there are other operations there.  But most will not chart strips they use.  There is no requirement to do so, and furthermore it doesn't really help with traffic avoidance, as during application runs the aircraft seldom even gets to TPA. Most operators will use 500 feet for enroute, as it keeps them low and out of everyone else's hair.

I have considered registering my grass strip, as it establishes prior use, and should there be zoning changes, it would be grandfathered.  Of course there are other ways of documenting that use, in the public record.
The power company story is also a good reason to have established prior use.
With wind turbines going up all over the place, it might provide some level of protection in terms of protection of an approach and departure path.
Addendum: There is a downside for registration and publication on a map, and that is when someone decides to use your strip, and has a problem. A local public use grass strip ran into that, and the owner did not have it properly insured as a public use airport. The financial consequences are not clear yet, but the headache is not one I would invite.

Then you obviously shouldn't register it for public use if you aren't going to do your due diligence.

The issue is not really registration, but whether it is flagged for Restricted use or not.  Some municipalities require registration, but most don't.  Having it Restricted means it's on the map when your friends are flying in, but flags it as not being available for public use.

Right but your answer reads like that isn't the obvious option... when it is.

Good point.  I wrote that answer quickly.  I will clean it up.  Thanks for the prod.


text:
What could cause a rear twin-jet's throttle to oscillate on descent?
I rode a smaller twin-tail-engined jetliner for a few short hops last month, and I noticed that their airport approaches are much rougher than the widebody airliners I am used to. I believe that it was an MD-80 with United Airlines.
As soon as the pilot began the descent, it seems like the he/she was going wild with the throttle; the engines would appear to idle for 10 seconds, then suddenly and audibly power to full for another 10 seconds, and the cycle would repeat until we were right above the runway. I know that this was not crew specific because I took the commercial flight on 6 different occasions on three different routes.
Question: Why did the pilots increase and decrease the throttle so rapidly and so many times on descent to the runway?
edit: Terrain: flat, Atlanta area; Meteorological conditions: heavy cumulus, twice during the night and the other four during dusk, light to moderate rain under and in the clouds. The clouds had no breaks and often had a strange formation where in some areas they would rise much higher than others. Imagine a series of mountains and valleys with several? miles of distance between cloud peaks and cloud dips.

without knowing the precise meteorological conditions I am afraid it will be hard to answer unambiguosly.

@Federico Does my edit clarify the conditions?

It would help if you know the aircraft type. Which airline / routes? I suspect a not so well tuned autopilot / autothrottle. Smaller jets often use generic autoflight systems which are tuned to the aircraft model. But it can also be meteorological effects above hilly terrain for example

The terrain itself was flat. I actually remember the make now, it was a McDonnell Douglas. The safety card said either MD-80 or MD-90.

I haven't much experience with those models. I have noticed a similar oscillation in Fokker 70 / 100 aircraft.

@DeltaLima That leads me to guess that this is, in fact, a rear twin-jet peculiarity.

Are you sure that it was the engines and not the air conditioning packs?

@Simon As the flight was filled only to 1/3 capacity (which really surprised me) I moved around from my wing seat to the rear, right next to the engine. It was definitely the engines, with the distinctive whining noise and rumble. Visually I could not tell if the spinner was faster or slower because of the low light, but the engine itself was situated less than 5 feet from my ears.

Possibly just a stepped descent: https://en.wikipedia.org/wiki/Continuous_descent_approach In the process of being phased out due to the increased noise and fuel consumption of repeatedly throttling up and down vs. cruising in on a direct line.

I think your note about this taking place in the Atlanta area with heavy Cumulus clouds in the area is the best clue as to why such large throttle inputs were necessary.  It sounds like there were thunderstorms in the area in the cumulus and mature stages.  The pilot was most likely encountering heavy updrafts and downdrafts passing through the air and had to compensate accordingly with the power levers to maintain approach airspeed and glidepath during the approach.


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Can manoeuvres like overbanking and high G braking be used in a single propeller aircraft?
While watching this very interesting short movie:

I noticed that for some turns pilot uses overbanking like at 1:25. Basically in a turns more than 90 of bank is used.
Can you explain how it works and how to use it and what is the advantage compared with regular steep turns?
I have CPL but I was never thought such maneuvering. Can it be used in SEP aircraft or glider with just a couple of G?
At the end of the movie looks like 5G is used for slowing airplane for landing. 5G is pulled and jet instantly slows from 300 to 260. I don't know if brakes are extended though. Can it be used in SEP as well? Like dive to the runway pull some G, slowdown and land?

Can you explain how it works and how to use it and what is the advantage compared with regular steep turns?

He needs to turn and start to descent. Note, that the two moments he's overbanking he's flying over ridges and wants to descent to the valley behind.
Now when you want to lower the nose in a turn you need to bank more so you still have the desired lateral lift, but less vertical.
But he's so fast that he needs negative vertical lift component, and since the wings are producing positive lift to make the turn, he needs to bank more than 90° to get it.

I have CPL but I was never thought such maneuvering. Can it be used in SEP aircraft or glider with just a couple of G?

It is a positive G manoeuvre and you can do the same with, say, 2G, so technically yes. However:

You have no use for it. He's flying 420–480 knots. At 420 knots, a 1G (meaning 1G lateral, so 1.41G total at 45° bank) turn will have rate 2.6°/s and radius 4759 m. But in a SEP you might be flying, say, 120 knots and then 1G turn will have rate 9.1°/s and radius 388 m. That, of course, applies to vertical turns as well. So where he needs to push -1G, and thus overbank, you would do with reducing to, say, 0.5G, and thus still normal side up.
You would probably loose spatial awareness rather quickly if you are not trained in aerobatics. The fighter pilots train a lot to be able to handle the plane at these high Gs and unusual attitudes. Without training, it will get confusing pretty quickly.
Your attitude indicator will likely tumble. The fighters have attitude indicators carefully designed not to, but your average mechanical one in something like C172 almost surely will. That is not a problem in itself—aerobatic pilots just cage it and fly purely on external references—but you need to be aware of it.
The fighter has a G-meter, but in a typical SEP plane you don't. But if you fly below $V_A$, the wing will stall before exceeding the structural limit, so you can do without.

During aerobatics, such, or similar manoeuvres may be performed. For example in Red Bull Air Race turns are usually executed at 90° bank (to use all the lift for the change of direction). The plane climbs a bit to store some speed in height, since turns are tighter at slower speed, then makes the hard turn, during which it has 0G vertical and the vertical speed decays and it changes from climb to descent and then it levels from the descent in the gate height and with all its speed back.

At the end of the movie looks like 5G is used for slowing airplane for landing. 5G is pulled and jet instantly slows from 300 to 260.

The induced drag is proportional to coefficient of lift. So when the wings are requested to generate a lot of lift, they also generate a lot of drag. Especially since this might have been enough to pull the delta wings of the Typhoon to the vortex lift regime, where it generates even more drag.
I believe part of the reason to fly such sharp turn here is to fly the pattern at modest size despite the high speed and the deceleration is just a nice side-effect. The speed brake would be enough to slow down, and still needs to be used as 260 knots is still about twice the landing speed.

Very interesting. Do you know anything about using G for slowing down?

Is there a small mistake? To have 1G lateral 60 degrees bank? Not 45?

@Andrius, added.

60° is 2G not 2.24!!! 1 / cos(60) = 2!

@Andrius, you are right, it is 2G total, not 2G lateral. Lateral at 60° is 1.73G. Lateral 1G at 45° was always correct though.

Another reason would be that pilots tend to dislike negative g-forces. Also, a fighter tends to have a -3 g limit while having a +6 to 9 g limit, so even if the roll would take time, one can still turn sharper. And it's more fun

Well, yes, one could fly it at negative G, but banking left to turn right and descend is even more confusing than overbanking to the right.

And the reason for disliking negative G is that the anti-G suit together with straining the right muscles is quite efficient at delaying black-out due to blood being pulled from head (especially eyes) during upward acceleration, but there is nothing to delay red-out due to blood being pushed to head (and eyes) during downward acceleration, since head can't be compressed and does not have much muscles to strain.

Just smile really really strong : )


text:
Flying sideways, how is it done?
I assume that the fuselage and tail fin can generate lift when flying sideways with a constant heading and a little pitch up (er, yaw right assuming left wing down) will introduce a vertical component to the thrust.
Is that all there is?  What else might be going on?

@fooot  Thanks.  it is a duplicate, I'll close.  Cheers.


text:
How are "expect" altitudes on STARs used?
STAR charts often have expected altitudes. For example:

This is, of course, different from mandatory crossing altitudes, and it seems a STAR with only expected altitudes would be insufficient for ATC to issue a descend via clearance, though I could be wrong about the second part.
Some charts say "VERTICAL NAVIGATION PLANNING INFORMATION" before the expected altitude, so my assumption is that these altitudes are strictly for planning purposes and allow a top of descent to be calculated.
My questions are:

When you enter the STAR in the FMS, will it pre-populate the expected altitude, and does this show up in the FMS exactly the same as a mandatory crossing altitude?
Are expected altitudes treated as suggestions by pilots or controllers? For example, in the above chart, if you were at JHAWK 15,000ft landing south, and Kansas City Center or Approach told you to "descend at your discretion, maintain 8000", would you (or the FMS) make any attempt to cross RUGBB at 12,000 even though it's not required?
How common is it for ATC to actually issue a "cross [fix] at [altitude]" where the fix and altitude are as expected on the chart? And, if it is common, why wouldn't it simply be mandatory?
Are expected altitudes part of lost communications procedures?
Am I missing anything with regards to the purpose of expected altitudes?

My questions are:
1) When you enter the STAR in the the FMS, will it pre-populate the expected altitude, and does this show up in the FMS exactly the same
  as a mandatory crossing altitude?

This depends on the model of FMS.  Some of them don't even have Vertical Navigation (VNAV), and it really depends on the exact model.  I will say that three of the most common FMS's that I have personally used (Universal, Collins, and Honeywell) all pre-populate the expected altitude and it shows up exactly the same as a mandatory altitude.
In any case, the FMS is advisory only.  Unless the pilot dials in the actual assigned altitude and selects a vertical mode on the autopilot, it isn't going to descend on its own.  So if ATC doesn't assign the crossing restriction, you may see your VNAV pointer come alive and watch as you fly through the vertical profile without capturing it and it would be perfectly normal.  If I am getting close to the point where I would like to descend to make a crossing restriction and haven't been given lower, I will sometimes ask the controller:  "Do you need me to make the crossing restriction at RUGBB today?".  This gives me an idea of what's to come or prompts them to give me the descent clearance.

2) Are expected altitudes treated as suggestions by pilots or controllers? For example, in the above chart, if you were at JHAWK
  15,000ft landing south, and Kansas City Center or Approach told you to
  "descend at your discretion, maintain 8000", would you (or the FMS)
  make any attempt to cross RUGBB at 12,000 even though it's not
  required?

An "expect" altitude is just that.  It is an altitude to expect, but it is not always actually assigned.  If it isn't, then you don't have to make it and since your example is at pilots discretion, you could descend at whatever rate you want.  You could cross RUGBB higher or lower than 12,000 ft and nobody would care.
In actual practice, they usually only do this in a few situations:

If they have to hold you up higher due to traffic and you can no longer make the crossing restriction, they will just give you a "descend and maintain" altitude, sometimes with a "good rate" tacked on.
It's a particularly slow time (late at night, etc.) and there isn't much other traffic to worry about.
There is an aircraft at, say 13,000 ft. so they tell you to descend and maintain 14,000 ft with the intention of giving you the crossing restriction once you pass the conflicting traffic.

In this last case, I would get down to 13,000 ft. in time to make the crossing restriction if they gave it to me, but it wouldn't be required.

3) How common is it for ATC to actually issue a "cross [fix] at [altitude]" where the fix and altitude are as expected on the chart?
  And, if it is common, why wouldn't it simply be mandatory?

Again, this depends on the procedure but it is quite common.  That's why they put them there so that you can plan on what is typically done.  There may be operational reasons (like two different procedures that intersect) which prevent them from issuing it every time, so they can't just make it mandatory.

4) Are expected altitudes part of lost communications procedures?

Surprisingly, no.  Not unless the controller has specifically cleared you to expect or cross it or "descend via" a procedure.

5) Am I missing anything with regards to the purpose of expected altitudes?

Not on this one!  In some cases, there is a speed restriction which is listed on a separate line from an expect altitude. In these instances, the speed is required whether or not the speed or altitude was verbally assigned, just by being cleared via the arrival. For example, on the SFO HADLY2 arrival, you are required cross EUGEN at 250 knots, whereas 11,000ft is only required if assigned by ATC.

Someone else will have to comment on whether the STAR in the FMS includes the altitudes as well.
You are right, "expected" altitudes are suggestions so that pilots know about when they will need to begin their descent. Instructions from ATC are the final word, so they would either say "descend via" or specify the altitude if they were using the "expected" altitudes.
ATC instruction to "cross [fix] at [altitude]" will depend on the traffic situation. Along busy approaches, it is fairly common. It's not mandatory because it's not always necessary. It is up to ATC to decide what altitude the pilots should be at, and it may not always be the "expect" altitude.

The “expect” altitudes/speeds are published so that pilots may have
  the information for planning purposes. These altitudes/speeds must not
  be used in the event of lost communications unless ATC has
  specifically advised the pilot to expect these altitudes/speeds as
  part of a further clearance.

Reference: AIM Section 4. Arrival Procedures


text:
Why are the altitudes on an RNP IAC shown on the point while for a conventional approach are parallel to the route? Is there an actual difference?
The RNP approach for LGIR runway 27 has the altitudes on some of the points underscored.

I had the impression (and I'm afraid I'm wrong) that these are "crossing restrictions" and the controller can use the "Cancel Level restriction at IR402" in order to waive the restriction. Though this phraseology in ICAO Doc 4444 16th edition is only found under the Clearances on a SID and Clearances on a STAR sections but not in approaches.
Furthermore, I tried to search for the ICAO chart legends that unfortunately don't go in any further detail. Annex 4 for example has this

Unfortunately I don't have access to the Aeronautical Chart Manual (Doc 8697) in order to see if there are more details there.
While searching, I found out that the Belgian AIP goes one step further and has an (on SID/STAR) comment next to each of the altitude descriptions. Curiously, the Upper and lower limit got away with it.
To make things even more complex, conventional procedures have similar altitude depictions but on the route and not on the point. From that, I got the impression that this is a MEA (minimum en-route altitude) or something similar, thus different from having the altitude on the point. For reference, older VOR procedure, same airport.

My question: what are the altitudes depicted on the two approach charts? Is it the same concept drawn differently (conventional vs RNP) or is it something else?

What do you mean by "semantics" and "drawn differently"?  An altitude with a line under it always means "at or above", per the table you posted in your question.  Are you asking why the number values themselves are different?

@MichaelHall No sorry, I wouldn't go in all that trouble just for that. I want to know why the former is on the point and the latter is parallel to the route. Hence the "semantics" part. For example why would the Belgian AIP say that the underscore means at or above only on SID or STAR? That pops the question, what does it mean elsewhere?

I would guess that it means that if you are not on the published SID or STAR that the altitude restriction does not apply, but I don't see any real reason to emphasize that point.  Anyway, it doesn't imply that the underscore means something different elsewhere, only that it applies to the SID or STAR.  Those are two very different things...

Remember that an RNP approach is not simply an overlay of the existing VHF-based approach, it is an all-new, “clean sheet” approach.  At almost 20 NM, your VOR positional error will be roughly 40% greater than your RNP positional error.  At the FAF the VOR will be about 20% less accurate than RNP.  Thus, the RNP’s altitudes reflect the improved clearance from terrain that the system provides.  I also suspect (not sure) that expressing them as crossing altitudes is more aligned with the logic in modern FMSes.

@MaxR Thanks adding this bit of information. The last sentence of your comment is what interests me: why not make a legacy procedure compatible to the modern FMSes? I reworded the question with the hope that it became more clear.

This is merely a difference between charting styles from old to new. This happens when a country changes their style which only affects newer procedures. The VOR RWY 27 was last updated in 2016:

The RNP RWY 27 was updated at the end of 2022:

In both cases, these are crossing/segment altitudes. If you look at the coding for the RNP, you will see that these apply at each waypoint:

*Edit: I highlighted the MAP, but that does not get shown in the plan view as it depends upon the aircraft category.

I appreciate the effort but unfortunately this doesn't answer the question. Plus it's more of a speculation as it doesn't cite any official documents. LGAV has conventional procedures updated on July 2021 and they still have the altitudes on the route, not on the point.


text:
Can the removal of a duty-free sales trolley result in a measurable reduction in emissions?
Recently, SAS announced that:

Withdrawing tax-free sales will reduce the overall weight of the aircraft, which in turn will reduce fuel consumption and emissions.

I could buy that this might be a polite way to say "we don't make any sales, consequently, the trolley with the items is just ballast; throw it away". It's not the first time that I hear it though: some time ago I remember an article in Aegean's Blue magazine about saving 15 tons of CO2 in one year just by replacing the pilots' flight bags with the electronic equivalent (EFBs). Unfortunately I don't remember in which issue was that.
Now assuming that a trolley weights approximately 25kg empty so let's say 30kg with the merchandise. The L/D ratio of a an Airbus A320 is 16,3 and thus a 30kg reduction in the weight will result in approximately 18,05N reduction in drag and and an equal reduction in the thrust required to maintain the same speed.
Compared to the ~150kN that 2 CFM56-5B4 produce in cruise, The 30 Kg reduction in weight will result in 0,00012% a 0,038% to 0,06% reduction in required thrust (depending on the aircraft gross weight), which seems like a drop in the ocean. Can this make a difference measurable by an airline company at the end of the month/semester/year/century?

It seems a perfectly reasonable question, and the discussion around it helps make clear what sort of things the author is asking about. If we can't have questions in which the author isn't perfectly certain about what to ask or how to go about asking it, what would be left would be pretty dull.

To those who try to close this as "opinion based", I removed the "or is it for publicity?" part. @John K I'm sorry if that invalidates your answer.

The opinion policy is zealously over-applied by a lot of the folks on here.  Half of what is posted here is opinion.  That is half the point; to gain knowledge from industry insiders, tribal knowledge and all that.  If everything posted has to be backed up by links to factual data, what the point?  Just look it up.

I'm fairly confident you could get more than 5kg of merchandise on a trolley, but I don't think I've ever flown SAS so don't know what they sell.  Anyway that wouldn't lead to more than a doubling of your estimated saving per trolley; larger aircraft may have more than one.  And of course they could use the space for other (equally heavy) things, saving nothing

@ymb1 Yes but there were a lot more attempts than that to close questions for being opinion based. See, relying solely on stats doesn't always help :)

This post is still answering it's own question. You asked if the reduction is measurable, and then you calculated the value, thereby proving it is measurable.

@zymhan a value which according to the highest voted answer at this moment, is wrong. So please stop writing disruptive comments on the thread. Also it's good to have in mind that paper calculations are usually different from reality.

I've created a post in Meta because this comment discussion is going off the rails. https://aviation.meta.stackexchange.com/questions/3828/trolley-weight-savings-question

@zymhan: It's possible to calculate many things that aren't measureable.  For instance, gravitational waves were calculated decades before anyone actually measured them.

90kg (200lb) rather than 30kg, per https://apex.aero/2017/08/27/dumping-duty-free-airlines-goodbye-retail-trolley "Jettisoning onboard duty-free retail items translates into an approximate 200 pounds in weight savings" - plus selling onboard means more trash to collect and process.

Yes, the removal of payload will result in a measurable reduction in emissions.
First, I have to correct some math: the engines don't run at 150 kN in cruise - that would indicate a L/D ratio of only 4-5, since a typical A320 weighs around 60 tons mid-flight (give or take 10). Fuel consumption is roughly proportional to weight, so 30 kg out of roughly 60,000 kg is a 0.05% reduction, not a 0.00012% one.
As to whether one would be able to move the throttle down exactly 0.05% to benefit from the reduced weight and leave everything else equal, no, not even the autothrottle is so precise.
But that doesn't mean fuel consumption is unaffected: the balance of an aircraft's weight, lift, drag and thrust always affects its energy. At the exact same throttle setting, the aircraft will climb a fraction of a percent faster, and so finish its climb and go to lower fuel burn at cruise a few seconds sooner. In cruise, maintaining the same flight level, it can spend a minute or two at a bit lower throttle, or trimmed a bit down, which will make it arrive a few seconds sooner.
This is fundamental conservation of energy: if less of it is expended in drag, then either the engines have to work less, or the aircraft will climb or accelerate. This happens all the time - an airliner in level flight doesn't stay in perfect equilibrium throughout, but corrects for energy changes every once in a while. Even if it doesn't change how much fuel is pumped into the tanks that particular day, the effect is cumulative across all sources and persistent through random variations.
Overall the effect of weight on fuel burn is proportionate. Depending on the distance, everything aboard an aircraft can consume 10% to 50% of its weight in fuel each flight. A very rough ballpark is that, over the life of an A320, each pound of operating empty weight will cost an extra ton of fuel.
To be more specific, given the A320's fuel burn of roughly ~2,500 kg/hour, adding the trolley requires an extra 1.25 kg of fuel per hour it's in the air. For a 4-hour flight, that's an extra 5 kg of fuel. Over the 60,000 flight-hours an A320 will serve in total, that's 72,000 kg of fuel. So behind that trolley is 3 large tank trucks' worth of fuel to keep it in the air, and ~225,000 kg of CO2 emissions.
As an aside, in-flight sales of random junk really serve the airline, not the passengers. The profit margin on these items can be up to 100 times the tiny profit margin on economy tickets themselves. With airports packed full of duty-free shops, there's no shortage of shopping opportunities on an air trip. Cramped and burning fuel for every item on board, whether it sells or not, aircraft don't make for a very efficient or practical storefront.
Airlines only make up for this inefficiency by exploiting their cabin crews as free salesmen. Of course, airlines' environmental consciousness tends to correlate strongly with the price of jet fuel, so once sales profit no longer covers the extra burn, it's time to go green.

But even a 0.05% reduction is too small for giving even barely noticeable difference, isn't it?

@trolley813 SAS owns mostly Boeing 737-800. Quick search shows it can produce 400 lbs of CO2 per flight. Leaving trolley out this gives 90g of CO2 reduction per flight. SAS flew 36 thousands times last year, and that gives 3.24 metric tons per year. Is it barely noticeable, you tell me.

@trolley813 0.05% is a lot when you're burning fuel at aircraft rates. I've added specific math to the answer. It comes down to two or three large tank trucks over the lifetime of an A320.

@Mołot It's still drop in the ocean. According to 2017 reports, the total amount of  CO2 emissions in the world was about 37 gigatons per year. Even if we multiply these 3.24 tons by the total number of existing aircraft in the world (despite this figure is per airline and not per plane), which is about 39000, we get a total emission reduction by less than 1/250000. So, the game is not worth the candles: this surely won't significantly improve the environment.

@trolley813 but there are thousands if not millions of little ways to make little change that could add up to huge improvement. Not making any of them because making only one will not help seems unreasonable approach to me.

@Mołot That figure seems off by two orders of magnitude - it should be 40,000 lbs, not 400.

@trolley813 "Worth the candles" is an opinion. How much difference does the ability of flyers to buy stuff they don't really need in-flight rather than in the duty-free shop make in the world average standard of living? SE isn't really about opinions, but personally I'd value it as even less than 1/250,000.

@Mołot the problem is that this creates a distorted perception. If SAS is perceived as being more environment-friendly for that .05% reduction, customers may take that as (part of) incentive to choose a longer stop-over flight with SAS, though a direct flight with a “dirtier” airline would actually save something like perhaps 10% or a train ride would save 80% (I'm making up numbers here). Even if only a handful of passengers ever fall for that miscalculation, then the tiny savings of the ditched trolley (even if you sum those over all SAS flights) will already be cancelled many times over.

400 lbs of CO2? I think you slipped a decimal point there...

@leftaroundabout The reality gets murky quickly there, doesn't it!  However, I think you need more than a handful of passengers.  The savings probably get handled more cleanly if we focus on the number of kg lifted into the air by the plane.  If the cart masses 30kg, and an average human masses 60kg, that says that if SAS has exactly one human who chooses to fly over some magically emission-free method for every other A230 flight, then they break even on emissions.  I think for more realistic numbers, there's still a savings.

@trolley813 the whole ocean is made up of drops.

@CortAmmon you can't assess an extra passenger's environmental impact by their mass. In practice, fewer passengers doesn't mean the planes will have more empty seats, it means (in the short term) the airline will lower prices to fill those seats up anyway and (longer term) it'll scrap routes to get back to profitability. So, it does in fact make more sense to think of each passenger as taking an equal share in the plane's total CO₂ emissions, i.e. on the order of 0.5% rather than 0.05%. But you're right, this still means “a handful” wouldn't be enough, but one for every ten flights would be.

Well, any reduction in Basic Operating Weight, which eliminating the trolley achieves, is an increase in efficiency, because anything not humans and their bags paying money, or kerosene, and not essential to getting from A to B, is ballast.  So there is value in forgoing 65lb of ballast and whatever cash income it brings in (I suspect the real reason is it doesn't bring in enough cash flow to be worth the hassle of administration) in the accumulated savings over many years.
You can be sure that the financial and operations organization of SAS did a business case on whether to keep it on or get rid of it.  Clearly the business case favoured the get-rid-of-it option.
And you always have to stick the word "emissions" in there because that gives you extra moral weight to prevent anyone from accusing you of a simple economic decision to cancel the service.

I think this is the correct answer. The bean counters determined it cost more to fly the merch around than they were making by selling it. They then got the marketing drones involved who came up with the "green" spin to make it sound good.

Also: Saving that 65 pounds of duty-free cart that is not generating revenue allows you to carry 65 pounds of extra cargo which is generating revenue. Of course, this wouldn't be reducing CO2 emissions, but it does increase profit. :)

That is kind of implicit in my post, but yes.  Take away ballast = more payload, which is what the airline would really have in mind.  In any case, I'm not a member of the CO2 bandwagon so that part is irrelevant to me and therefore, increased profit = good news.

I paid for a flight Amsterdam to Accra this afternoon.
I selected the option to "Benefit from CO2-neutral travel".

fly CO2 neutral
Contribute directly to reforestation and conservation of tropical forest in Panama: this project promotes the restoration of ecosystems and biodiversity, and supports local development.
CO2 compensation for your flight costs:
GBP 5.80 [why in GPB, I don't know, I paid for the flight in Euros]
How did we get to this amount?
The calculation goes like this: by burning 1 kg (2 lbs) of fuel, 3.157 kg (6.959 lbs) of CO2 is emitted. So we start by determining the fuel consumption for your flight. This depends on the type of aircraft, distance flown, and number of passengers. Then, we calculate the average CO2 emission per passenger over a period of 3 months. This is how we calculate the amount you will have to pay to compensate for your share.

Now, flying my ~70 kg body plus ~10 kg of luggage to Accra and back consumes an additional X kg of fuel, and therefore emits about 3.157 * X kg of CO2.
The amount of extra fuel it costs may be relatively small, and it may well be a rounding error in each particular flight (a tailwind, or a couple of circuits of a holding pattern, may far outweigh any difference I could make), but it's a determinate and well-known amount (well-known by the airlines, that's for sure), and it corresponds to a determinate quantity of CO2 emissions.

There is one very important difference to note here, though. The calculation that the airline is using here is dividing the total gross weight of the aircraft by the number of passengers to get a share of CO2 emissions per passenger. This is a very different number from the marginal CO2 emissions of a plane that is flying anyway carrying an extra x kg of mass (whether person or duty-free cart,) as the weight of the passengers is quite small compared to the gross weight of the entire aircraft.

Or, put more simply, they're charging you the CO2 emissions for ~700,000 lb gross aircraft weight / 400 pax = 1,750 lb, not just your extra ~175 lb of yourself + baggage.

The other answers are correct, but too much on saving fuels.
Duty free trolleys are much more then just your 60 kg:

it should be handled and refill in various airports, it should be stored not only safely, but also securely (did you notice keys, and crew members have to sign some paper?
money handling. This needs a lot of papers, also accountants, and crew should be handled with cash. Logistically it is not simple, and delay the ever shorted airport times.

Then public relation will find some good words to justify cuts. It was so also for the slim seats, for not having anymore small bottles and cans for beverage (which were a lot quick to serve), or to reduce, to remove magazines. Reducing emissions make them to be seen as angels.

Obviously it will reduce fuel consumption and emissions, if only by a tiny fraction. Which is good! But that is not the reason for their decision. They have simply decided that the service is losing them money.
I get a bit irked by such pronouncements, because it seems to me that they are taking me for an idiot. It's like hotels and towels. When I was a young man, hotels would replace all your towels every day. Now most of them ask you to leave your towels on the rack if you haven't used them, and they will only replace the towels on the floor. That's fine by me; but they justify it as being motivated by a desire to save water, for the sake of the environment. Yeah, right.

water isn't free, so saving water IS saving money. Also, there's the cost of heating the water for laundry, the detergents, the cost of drying the towels after laundering, and the simple fact that in many areas, water conservation is a legal requirement due to limited supply. This is especially true in many popular resort locations, where salt encroachment is a serious problem. Considering the impact of your business practices on the long-term feasibility of your business model is being smart, not being trendy.

I think it’s a combination of factors: fuel saving not being the first reason, it certainly is a good motivation these days.
Then there are the logistics described above, costs due to security handling, thefts, percentage given to flight attendants, magazine printing costs, its weight and logistics handling.
And, obviously, the lessening interest of passengers in purchases. Airports have become shopping malls, and the 6-7 duty free retailers that cover 85% of the airports are also the same that provide the service on board airlines. So there’s really no competition, airlines produce the traffic and the Travel Retailers are making the money from this traffic avoiding to share it with the real ‘owners’ of the passenger traffic. Until 15 years ago, when airports duty free shops where not yet so huge and appealing, on board Sales conversion was 10% minimum. Now it’s down to 2% max. This says it all, in my opinion.

Based on the other answers, I think the actual answer is No, the difference to emission is not measurable. None of the instruments concerned are sufficiently accurate.
I don't think the engines even have instruments to measure CO2 emissions. The fuel gauges may have enough digits to display a 0.05% change, but they probably aren't calibrated that accurately. Even if you did fit super-precise instruments, you couldn't control for all the other factors that effect fuel consumption.
However, the difference is still possible to estimate, as proved by the people who have done so in this question. When multiplied over a large fleet and a year of operations, it's probably quite accurate.

I am pretty sure that the accountants can measure annual fuel consumption with 0.05% accuracy, since they're getting the bills. And since carbon in=carbon out, that also means they know exactly how much CO2 is produced.

@  MSalters - Yes, but how would they be sure that it was caused by removing the drinks trolley, and not passenger weight or headwinds? Or even that the fleet, routes and number of flights have changed from one year to the next?

@RobinBennett because they know that the trolley weights precisely x Kg for each flight. Even if I am on that flight and weigh precisely x Kg more than the average adult passenger (which is what they'll calculate W&B with), removing the trolley is still x Kg less being carried from A to B. I agree, that headwinds, holding patterns, etc. will burn more fuel, but removing that x Kg from the plane will burn less fuel given all the considerations for that flight.

@FreeMan, I'm not sure what you're saying. Just because the plane burns less fuel doesn't mean that you can measure the difference, because you don't have an identical flight to compare it against.

But you can calculate, for any given flight, how much fuel each Kg cost. Multiply that fuel cost times the x Kg the trolley weighs and you'll know how much you spent by having it on board, or saved by not having it on board.

@Freeman, that's exactly what I said in my answer. Calculating is not the same as measuring.

@RobinBennett I understand what you're saying, that in any given single flight, many variables will impact fuel consumption, and the impact of a single trolley may be subsumed in the background noise of other random effects. That's likely true, but it doesn't preclude measurement, just one specific type of measurement. ALL measurements are estimates, because no instrument is perfect.


text:
Why is the 60-year-old NK-12 more fuel efficient than Europrop TP400?
If Wikipedia is correct the 60 years old NK-12 is more fuel efficient than the Europrop TP400, the engine for the Airbus A400M transport aircraft.
For the NK-12MV a specific fuel consumption of 0.219 kg/kW-hr is given.
The TP400 has a specific fuel consumption of 0.238 kg/kW-hr according to Wikipedia.
Am I interpreting these specifications wrongly?

Can you provide some figures?

The source of the Specific Fuel Consumption in Wikipedia is unclear. I have found a paper (PDF) that discusses the efficiency of shaft power off-take (that is using engine power to drive systems such a electric and hydraulic generators instead of delivering propulsion).
It mentions the TP400-D6 (which is installed on the Airbus A400M) has a SFC of 0.167 kg/(kW.h) for shaft power off-take and a SFC of 0.213 kg/(kW.h) for delivering propulsive power. This means that the TP400 is more efficient than the Wikipedia article presents and more efficient than the SFC of the NK-12 presented by Wikipedia.
It also shows that the TP400-D6 is more efficient in delivering shaft power than in delivering propulsive power.

Age of design
It is likely that the design of a newly manufactured NK-12 differs significantly from the original designs produced 60-years ago. So we are not really comparing the TSFC of an original 1950's NK-12.
Speed
Wikipedia's source for the NK-12 quotes a "TO" figure - presumably TSFC at take-off power.
Wikipedia doesn't identify a source for it's (T)SFC figure for the TP400. The makers of the TP400 don't publish SFC figures.
TSFC increases with speed. Many published TSFC figures are for cruise speeds.
Props
I imagine efficiency depends somewhat on application, and this must include propeller design.
It might be that there are factors other than fuel-efficiency that affect propeller design. For example, noise may not be a factor for most military applications but it would affect civil applications.
Both these engines were designed for military applications but there may have been some difference in prioritisation of these and other factors.
Conclusion
I don't think it has been clearly shown that the NK-12 is more efficient than the TP400 (though it may well be).

Knowing the speed at which the SFC figure is measured is key. BTW, I think the question is not about one particular engine which is 60 years old, but about the design per se, considering that materials and processes back then allowed lower compression ratios and turbine entry temperatures than today.


text:
Is there any reason to have ADS-B out that is not based on GPS?
The ADS-B system is only as accurate as the location data source it uses. In the US the 2020 ADS-B mandate requires that horizontal location data be from a GPS source with minimum performance standards set out in 14 CFR § 91.227.1
The aircraft in the Lamia crash in Colombia had ADS-B out that was based on an inertial system resulting in their ADS-B track being off from their actual position. It was off by 2 km when the flight began and drifted further during the flight, possibly being off by as much as 4 km by the time of the accident.2
Although ATC radar will still get an accurate location from the transponder, other aircraft might be using the data for traffic advisories through a system like ATAS. Using a system that could be sending inaccurate data has the potential to be dangerous.3 No info would be preferable to incorrect info. Is there any reason to install an ADS-B out system that does not use a GPS data source?

1ADS-B Frequently Asked Questions (FAQs)
2Satcom Guru: LMI2933 LAMIA AVRO RJ85 Medellín Deadstick
3At this point there is no reason to believe inaccuracy of location data had any bearing on the LMI2933 accident.

BTW, source 2 in the question is a fascinating read. He did a pretty thorough analysis of the ads-b data in the accident.

No, there is no reason to do this, as the FAA will not currently provide type certificates to ADS-B equipment that does not meet or exceed 91.227, (TSO-C166b and TSO-C154c). There is already one case where the FAA has recinded the type certificate for ADS-B equipment for uncomplying hardware (Navworks has words too). This results in a huge waste of money on the part of the owner, as the aircraft is not compliant for airspace requiring ADS-B.

@RonBeyer Wow, That's quite a snafu!

Not only that, but the FAA is recommending that owners not only deactivate the equipment, but have it removed. They effectively grounded all the aircraft with this equipment installed because now you have non-TSO avionics installed in a certified aircraft. This is the reason that my aircraft is getting a Garmin GTX345 from a major manufacturer rather than a start-up bargain ADS-B.

@RonBeyer I guess you get what you pay for. Everybody's gotta start somewhere, though. I used to deliver to Garmin when they were working out of a small warehouse in Lenexa KS

There are still quite a lot of aircraft that do have ADS-B based on inertial navigation position.
The reason for this is quite simple; they don't have GPS or the GPS is not connected to the transponder. Somewhere during the lifetime of the aircraft the transponder has received an update or has been replaced and is now transmitting ADS-B messages, based on the only position source available to the transponder; the Inertial Navigation System. That is fully legal, but it does not meet the ADS-B requirements of the various ADS-B mandates around the world.

Is this a danger to the safety of flight when ADS-B IN based systems like ATAS are used?
No, not at all. ADS-B IN systems do not use the data from these aircraft as the ADS-B messages contain several quality indicators that must meet certain conditions before a track is being displayed in the cockpit. Transponders transmitting INS positions indicate that the position integrity and accuracy is very low. In addition the source integrity level (SIL) will also be set to 0. Each of these indicators will result in the track not being displayed.


text:
Is the airport capacity related to number of runways?
Lets say two different airports have the same number of runways, and terminals capable of handling any number of passengers. I realise that year round climate may have an effect on the number of days that planes may be able to land. But are there any other major factors which are able to make a big difference to the number of passengers those airports would be able to process?
For example, do the placement of runways interfere with air traffic control?
If both make maximum use of their capacity, is it likely that both would have very similar numbers of annual passengers?

As far as number of annual passengers, that's determined more by "What airline(s) have a hub there?," "How many people need to fly to or from this city?," and "How centrally-located is this city between places people want to go?" Nashville, for example, has more parallel runways than many much busier airports have total runways. But it's not a major hub to any airline (unless you count the Southwest "focus city" designation) or located in a very large city, so it doesn't get nearly as much traffic. The airport is capable of handling a lot more pax than it actually does.

Your title doesn’t seem to match your actual question.

Airport Capacity
At major airports the capacity of the system of runways is the most restricting element. While it is usually possible to increase capacity of the other airport elements or adding a new runway (plus associated taxiways) is very expensive and takes a very long time to complete.
The runway capacity is the principal cause of most extreme instances of delays that lead to widespread schedule disruptions, flight cancellations and missed flight connections. The runway capacity varies greatly from day to day and changes are difficult to predict (even a few hours in advance).
Factors:
The capacity of the runway system depends on several factors, the most important ones:

Mix of aircraft classes using the airport: the aircraft mix indicates composition of aircraft fleet that is using any particular runway (e.g. 25% S, 60% L and 15% H).
Separation requirements imposed by the ATM system: due to wind tip vortices, leading aircraft and trailing aircraft must be separated by a determined distance (Heavy aircraft are the ones that produce more wake turbulence).
Type and location of exits from the runway: trailing aircraft of any pair cannot touch down on the runway before leading aircraft is clear of the runway. High-speed runway exits (also well placed runway exits) reduce runway occupancy times for arriving aircraft.
Mix of movements on each runway and the sequencing of the movements: specified for all combinations of consecutive operations (arrival-departure). There's an important trade-off between maximum arrival and departure rates that an airport can achieve.
Lateral separation: (especially in bad weather) between aircraft approaching the same airport on parallel runways.
Sequencing and separation of departing and landing aircraft on runways that intersect.
Sequencing of aircraft approaching airports located in close proximity to one another, where one aircraft must cross the path of another aircraft landing at a nearby airport.
Direction and strength of winds.
Noise-related and other environmental considerations and constraints.

Conclusion:
It is difficult to predict the capacity of the runway system of an airport, so it is difficult to compare two airports with similar runway characteristics, since the factors depending on the airport capacity involve different design and operational parameters. Furthermore, everything is subject to the important probabilistic factor, the weather, which makes the prediction and comparison of airport capacity even more difficult.

The FAA has a model to forecast capacity based on several of these inputs.  I knew some folks that used to do this a couple decades ago to plan infrastructure improvements at airports.  https://www.faa.gov/airports/planning_capacity/runwaysimulator/

This is a complicated question to answer but I'll try my best to give you an idea.
When you say number of runways there are a few situations; this will vary based largely on wind as well as when and where the airport was built, but there are two main cases to consider. Keep in mind the wind may prevent the use of certain runways.
1: Side by side runways. Large airports like KPHL, KJFK, KORD (and even places similar in size to Van Nuys Airport) have parallel runways. This can greatly aid in throughput as two planes can land/takeoff simultaneously
2: Intersecting Runways. In this case you still have two runways but they will cross each other and depending on aircraft size cannot be used simultaneously. If the airport supports GA or the runways intersect towards their respective ends a land and hold short may be possible. With intersecting runways you would, in theory, have less options since you can't have the simultaneous situation you do with parallel runways.
Other Factors
Aircraft Size: another thing to consider is runway length and aircraft size. Generally speaking runways at a given airport are often of different sizes. As such some aircraft may require a specific runway, if, on a given day you happen to only be landing large aircraft you may only be able to make use of one of your two parallel runways even though both are useable in the current wind.
Taxi Ways: for what it's worth I would not think taxi ways are a limiting factor in airport design. They often are the place where the queue builds up but generally are not the cause of the queue.
Ground Crew/Ground Resources: If we are talking strictly commercial operations it takes time and resources to turn a plane around (get it back in the air). The plane may need fuel or a de-ice (de-ice facilities have gotten better and are usually near the runway now). You may need a tug, a crew to load the plane, food, cleaning … you get the idea.
Physical Obstacles: Some airports are built in areas with tough terrain. This may cause all departures and takeoffs to come in from a single direction. This can limit the amount of traffic in and out of an area as well.
Noise Abatement: With the growing concern for local communities and increasing noise of jet engines, some airports have growing restrictions on when you can and can't take off. I fly out of KPNE and they have restricted runway use on Sundays as well as no touch and go's at various times. In this case two airports with the same number of runways may have different throughput due to runway restrictions.
Runway Approach Systems: Not all airports have instrument approaches on all runways (or any runway for that matter, although with the addition of GPS approaches, more and more airports have some kind of approach). If the weather is bad the better equipped airport will always have a greater throughput (an ill-equipped airport may prevent landings all together, although that's unlikely for commercial airports these days).
The locale is a big factor as well; if you build a huge airport in an area that no one wants to go to or leave, it's not going to see much traffic. Likewise if you build a tiny airport in Central Park, chances are you will have a stream of planes heading to and from the Hamptons in the summer….

In brief, parallel runways are built to increase capacity, intersecting runways are built to increase usability (i.e. crosswinds).

I'm sorry, but I don't see how this adds anything to the already existing (almost 3 years old) answers

@Federico The brevity has something going for it, IMO.


text:
What are the rules in the UK about attaching a GoPro camera to the outside of an aircraft?
Is it fully legal to have a GoPro attached to the outside of the aircraft during flight, in the UK? I've heard mixed answers, but I don't want to try it until I've got confirmation.

Related: http://aviation.stackexchange.com/questions/96/can-i-attach-a-camera-to-the-outside-of-my-aircraft

Great question. I've wondered about this for a while, but @bjb568's referenced answer is a complete answer to this question.

The discussion is the same in Germany. One party says that attaching a camera to your aircraft is an alteration which render's the aircraft without certification. Another party says it's fine, because it's not permanent. You will however have another issue, which is: What happens when the camera detaches and damages property or pedestrians on the ground? Your insurance will most likely not cover this....

For those voting to close as duplicate, please note that the other question asks about FAA regulation. This question is specific to the UK where the UK-CAA is the regulating authority. So this is in fact a different question.

On its way to damaging people and property on the ground, a detaching camera could also wreak havoc on the aircraft itself.

Flyer magazine had an article on this recently. I've not been able to find the full article on their website, but I have found this which at least partially answers your question.
https://www.flyer.co.uk/gopro-camera-mounts-to-be-approved-by-engineer/
From the article, which was published in Feb 2016:

Mounting a camera is a modification, and requires either inspection from a Part66 licensed aircraft engineer, or via the CAA as a minor modification.
To approve any installation the engineer will need to complete a maintenance release checklist and complete the aircraft logbook entry.
If your aircraft is overseen by the British Microlight Aircraft Association or Light Aircraft Association, then their restrictions apply (but it doesn't say what those are).

It also references CAP1369, which is the CAA document covering mounted cameras. I'm including a link to that here.
CAA CAP1369

welcome to aviation.se Please do not post only a link, the page could disappear any time. Instead, write in your answer the part that is relevant to the question.

The Certificate of Airworthiness may be invalidated with an external attachment to the aircraft.  The aircraft operator will need to inquire to the CAA what applies for the type in question.  This is the operators best course of action to get an answer on airworthiness questions.
However it may just require pilot approval, but it depends, there are however precedence in photography fields already pertaining to external fasteners and equipment. But contacting the CAA is the best way to clear this up.


text:
Where is the formal ICAO flight plan text format specified?
I want to write a parser for ICAO format flight plans, like the one shown below.
(FPL-AEE036-IS -A320/M-SCDE2GHILORTUWY/S -LGTS1635 -N0471F310 LEKPO UL617 SKP UB1 ABLON -LGAV0042 LGSA -PBN/C1B2S1 DOF/160805 REG/SXDVD)
The thing is that everything I come across is related to flight plan filling and not about this format, what to expect, what not to expect, field meanings, possible values etc.
I am looking for something like that but formal, preferably from some ICAO document

You will want to look in PANS-ATM (ICAO Document 4444), specifically, Appendix 2. (reproducing the entire appendix in this answer is not practical; it is 10 pages long). SKYbrary is also a nice resource.
Note that the ICAO model flight plan form actually contains the text format embedded in the form. Where slashes, hyphens, prefix letters etc. are required, they are printed directly on the form. I have highlited a few in the below screenshot for clarification:

<<≡ denotes start/end of message and newline.
➝ denotes a space.

Makes sense after all. Being a developer, I was expecting to see something like the CSV RFC. But what you've posted looks like the closest thing to what I've asked.